1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a touch sensing type LCD device including an anti-static layer and a method of fabricating the same.
2. Discussion of the Related Art
Recently, LCD devices have been widely used as a technology-intensive and value-added device of next generation due to their low power consumption and portability. In general, an LCD device uses the optical anisotropy and polarization properties of liquid crystal molecules to produce an image. Due to the optical anisotropy of the liquid crystal molecules, refraction of light incident onto the liquid crystal molecules depends upon the alignment direction of the liquid crystal molecules. The liquid crystal molecules have long thin shapes that can be aligned along specific directions. The alignment direction of the liquid crystal molecules can be controlled by applying an electric field. Accordingly, the alignment of the liquid crystal molecules changes in accordance with the direction of the applied electric field and the light is refracted along the alignment direction of the liquid crystal molecules due to the optical anisotropy, thereby displaying images.
Because the LCD device including a thin film transistor (TFT) as a switching element, referred to as an active matrix LCD (AM-LCD) device, has excellent characteristics of high resolution and displaying moving images, the AM-LCD device has been widely used.
The AM-LCD device includes an array substrate, a color filter substrate and a liquid crystal layer interposed therebetween. The array substrate may include a pixel electrode and the TFT, and the color filter substrate may include a color filter layer and a common electrode. The AM-LCD device is driven by an electric field between the pixel electrode and the common electrode to have excellent properties of transmittance and aperture ratio. However, because the AM-LCD device uses a vertical electric field, the AM-LCD device has a bad viewing angle.
An in-plane switching (IPS) mode LCD device or a fringe field switching (FFS) mode LCD device may be used to resolve the above-mentioned limitations. FIG. 1 is a cross-sectional view of an IPS mode LCD device according to the related art. As shown in FIG. 1, the array substrate and the color filter substrate are separated and face each other. The array substrate includes a first substrate 10, a common electrode 17 and a pixel electrode 30. Though not shown, the array substrate may include a TFT, a gate line, a data line, and so on. The color filter substrate includes a second substrate 9, a color filter layer (not shown), and so on. A liquid crystal layer 11 is interposed between the first substrate 10 and the second substrate 9. Because the common electrode 17 and the pixel electrode 30 are formed on the first substrate 10 on the same level, a horizontal electric field “L” is generated between the common and pixel electrodes 17 and 30. The liquid crystal molecules of the liquid crystal layer 11 are driven by a horizontal electric field such that the IPS mode LCD device has a wide viewing angle.
FIGS. 2A and 2B are cross-sectional views illustrating turned on/off conditions of an IPS mode LCD device according to the related art. As shown in FIG. 2A, when the voltage is applied to the IPS mode LCD device, liquid crystal molecules 11a above the common electrode 17 and the pixel electrode 30 are unchanged. But, liquid crystal molecules 11b between the common electrode 17 and the pixel electrode 30 are horizontally arranged due to the horizontal electric field “L”. Because the liquid crystal molecules are arranged by the horizontal electric field, the IPS mode LCD device has a characteristic of a wide viewing angle. FIG. 2B shows a condition when the voltage is not applied to the IPS mode LCD device. Because an electric field is not generated between the common and pixel electrodes 17 and 30, the arrangement of liquid crystal molecules 11 is not changed.
In the FFS mode LCD device, one of the pixel electrode and the common electrode has a plate shape in the pixel region, and the other one has an opening. The pixel and common electrode are formed on a lower substrate. As a result, liquid crystal molecules are driven by a fringe field between the pixel and common electrodes.
Unfortunately, because there is no common electrode formed of a conductive material on an upper substrate in the IPS mode LCD device or the FFS mode LCD device, an anti-static layer, which is formed of a transparent conductive material such as indium-tin-oxide (ITO) and indium-zinc-oxide (IZO), is required on an outer side of the upper substrate to prevent problems resulting from a static electricity. Generally, the anti-static layer has a thickness of about 200 angstroms (Å) and a sheet resistance of about 500 ohms per square (Ω/sq). because the sheet resistance of the anti-static layer is substantially the same as that of a metallic material, there is no damage on the device from the static electricity due to the anti-static layer.
The IPS mode LCD device or the FFS mode LCD device are used for a television, a projector, a mobile phone, a PDA, and so on. Recently, mobile devices include a touch sensor such that the device can be operated by touching.
Unfortunately, even if a capacitive overlay type touch sensor is included in the cell of the IPS mode LCD device or the FFS mode LCD device, a change of capacitance generated by a touch may not be detected because of the anti-static layer, which is formed of the transparent conductive material such as indium-tin-oxide (ITO) and indium-zinc-oxide (IZO), of the IPS mode LCD device or the FFS mode LCD device. Thus, the related art IPS mode LCD device or the FFS mode LCD device may not be operated with a touch sensor.
In more detail, when the user touches his finger onto the IPS mode LCD device or the FFS mode LCD device, the capacitance is generated between the finger and the anti-static layer of the IPS mode LCD device or the FFS mode LCD device. The capacitance is discharged into an outer space through the anti-static layer such that the touch of the user can not be detected by the capacitive overlay type touch sensor. If the anti-static layer is removed for touch sensing, there may be damages to the IPS mode LCD device or the FFS mode LCD device from static electricity.